MULTILAYER COATING FILM AND COATED OBJECT

Abstract

A multilayer coating film 12 includes a bright layer 15 and a colored layer 16 superposed on the bright layer 15, the bright layer 15 including aluminum flakes 22, and the colored layer 16 including a black pigment 23 dispersed in the colored layer 16. The black pigment 23 in the colored layer 16 has a particle size distribution with a peak at a particle size of 200 nm or lower.

Claims

1. A multilayer coating film comprising a colored layer superposed on a bright layer, the colored layer being translucent and including a black pigment dispersed in the colored layer, the bright layer being superposed on a black base layer, the bright layer being a coating film including a bright material, the black pigment in the colored layer having a particle size distribution with a peak at a particle size of 200 nm or lower, and the black pigment in the colored layer having a concentration ranging from 0.2% by mass to 0.4% by mass inclusive.

2. (canceled)

3. The multilayer coating film of claim 1, wherein the black pigment in the colored layer is carbon black.

4. (canceled)

5. The multilayer coating film of claim 1, wherein the bright material is aluminum flakes.

6. The multilayer coating film of claim 5, wherein the aluminum flakes are vapor-deposited aluminum flakes.

7. (canceled)

8. The multilayer coating film of claim 1, wherein a transparent clear layer is superposed on the colored layer.

9. A coated object comprising the multilayer coating film of claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] FIG. 1 shows a structure.

[0029] FIG. 2 shows visible light transmittance of a coating film which employs conventional carbon black as pigment.

[0030] FIG. 3 is a cross-sectional view schematically showing Rayleigh scattering in a coating film in the case of large pigment particles.

[0031] FIG. 4 is a cross-sectional view schematically showing how Rayleigh scattering is reduced in a coating film in the case of small pigment particles.

[0032] FIG. 5 is a cross-sectional view schematically showing an example multilayer coating film provided on a surface of a car body.

[0033] FIG. 6 is a graph schematically showing a particle size distribution in commercially available carbon black and in fine carbon black.

[0034] FIG. 7 is a graph schematically showing a particle size distribution in fine carbon black according to an example.

[0035] FIG. 8 is a graph showing spectral reflectance of a multilayer coating film according to the examples and a comparative example.

DESCRIPTION OF EMBODIMENT

[0036] Embodiments of the present invention are described below with reference to the drawings. Note that the below embodiments are merely beneficial examples in nature, and are not intended to limit the scope, application, or uses of the present invention.

[0037] As shown in FIG. 5, a multilayer coating film 12 provided on a surface of an automobile body (steel plate) 11, contains a black base layer 14, a bright layer 15, a translucent colored layer (black) 16, and a transparent clear layer 17 which are superposed one upon the other in this order. An electrodeposition coating film (undercoat) 13 is formed on the surface of the automobile body 11 by cationic electrodeposition. The multilayer coating film 12 is provided on top of the electrodeposition coating film 13. In the multilayer coating film 12, the black base layer 14 corresponds to an intermediate coat, and the bright layer 15, the colored layer 16, and the transparent clear layer 17 correspond to a topcoat.

[0038] A first black pigment 21 is dispersed in the black base layer 14. Aluminum flakes 22, which serve as bright material, and a second black pigment 23 are dispersed in the bright layer 15. The second black pigment 23 is dispersed in the colored layer 16.

[0039] Commercially available carbon black, graphite, or iron (II, III) oxide may be employed as the first black pigment 21. It is beneficial to employ fine carbon black as the second black pigment 23.

[0040] As shown in FIG. 6, commercially available carbon black usually has a particle size distribution with a peak at a particle size ranging from 300 nm to 500 nm inclusive. The fine carbon black acting as the second black pigment 23 in the bright layer 15 and the colored layer 16 has a particle size distribution with a peak at a particle size of 200 nm or lower. It is beneficial if the fine carbon black has a small particle size. However, too small particles are prone to clump together (dispersion properties deteriorate), which is why it is advantageous if the peak particle size has a lower limit of, e.g., 50 nm.

[0041] Fine carbon black can be obtained by wet grinding commercially available carbon black using a grinding medium such as glass beads. By wet grinding, the structure of the carbon black is mechanically ground and obtains a small particle size.

[0042] In order to develop a grey color, the colored layer 16 has a pigment concentration (carbon black) ranging from 0.1% by mass to 0.5% by mass inclusive. The black base layer 14 serves as a black base, and thus has a pigment concentration ranging from, e.g., 1% by mass to 20% by mass inclusive.

[0043] The aluminum flakes 22 in the bright layer 15 are oriented to be substantially parallel with the surface of the bright layer. After having applied a coating, which includes the aluminum flakes 22 and the second black pigment 23, on top of the black base layer 14, a solvent included in the coating film is vaporized by stoving. As a result, the coating film shrinks in volume and becomes flat, and the aluminum flakes 22 arrange in a physically flat manner.

[0044] The black base layer 14 includes a resin component which may be, e.g., a polyester-based resin. The bright layer 15 and the colored layer 16 include a resin component which may be, e.g., an acrylic-based resin. The clear layer 17 includes a resin component which may be, e.g., an acid/epoxy-based cured acrylic resin.

Examples and Comparative Example

First Example

[0045] The composition of a multilayer coating film of a first example is shown in Table 1.

TABLE-US-00001 TABLE 1 Solid Content Coating Film by Mass Thickness Layers Resins and Other Components (%) (μm) Transparent Resin: Acid/Epoxy-Based Cured 100 35 Clear Layer Acrylic Resin Colored Layer Resin: Acrylic-Based Resin 99.7 10 Pigment: Fine Carbon Black 0.3 (Peak Particle Size: 180 nm) Bright Layer Resin: Acrylic-Based Resin 68.0 2 Pigment: Fine Carbon Black 7.0 Bright Material: Vapor-Deposited 25.0 Aluminum Flakes Base Layer Resin: Polyester-Based Resin 65.7 15 Pigment: Commercially Available 7.1 Carbon Black Extender Pigment: Barium Sulfate 27.2

[0046] After having employed the wet-on-wet method to apply each coating, namely the black base layer, the bright layer, the colored layer, and the transparent clear layer, onto a steel product, the layers are stoved (heated at 140° C. for 20 minutes). FIG. 7 shows the particle size distribution of the fine carbon black used. As FIG. 7 shows, the fine carbon black has a particle size distribution with a sharp peak at a particle size of 180 nm. The aluminum flakes in the bright layer have a particle size ranging from 10 μm to 30 μm inclusive when viewed in plane, and a thickness ranging from 0.1 μm to 2 μm inclusive.

Second Example

[0047] The composition of a multilayer coating film of a second example is shown in Table 2.

TABLE-US-00002 TABLE 2 Solid Content Coating Film by Mass Thickness Layers Resins and Other Components (%) (μm) Transparent Resin: Acid/Epoxy-Based Cured 100 35 Clear Layer Acrylic Resin Colored Layer Resin: Acrylic-Based Resin 99.7 10 Pigment: Fine Carbon Black 0.3 (Peak Particle Size: 180 nm) Bright Layer Resin: Acrylic-Based Resin 68.0 2 Pigment: Fine Carbon Black 7.0 Bright Material: Vapor-Deposited 25.0 Aluminum Flakes Base Layer Resin: Polyester-Based Resin 71.3 15 Pigment: Commercially Available 3.6 Carbon Black Pigment: Titanium Oxide 13.7 Extender Pigment: Barium Sulfate 11.4

[0048] In the second example, the base layer is grey, whereas the other aspects of the composition are the same as in the first example.

Comparative Example

[0049] The composition of a multilayer coating film of a comparative example is shown in Table 3.

TABLE-US-00003 TABLE 3 Solid Content Coating Film by Mass Thickness Layers Resins and Other Components (%) (μm) Transparent Resin: Acid/Epoxy-Based Cured 100 35 Clear Layer Acrylic Resin Colored Layer Resin: Acrylic-Based Resin 99.7 10 Pigment: Commercially Available 0.3 Carbon Black (Peak Particle Size: 400 nm) Bright Layer Resin: Acrylic-Based Resin 68.0 2 Pigment: Commercially Available 7.0 Carbon Black Bright Material: Vapor-Deposited 25.0 Aluminum Flakes Base Layer Resin: Polyester-Based Resin 71.3 15 Pigment: Commercially Available 3.6 Carbon Black Pigment: Titanium Oxide 13.7 Extender Pigment: Barium Sulfate 11.4

[0050] In the comparative example, commercially available carbon black (peak particle size of 400 nm) is employed as pigment in the colored layer and the bright layer. The base layer is a grey layer. The other aspects of the composition are the same as in the first example.

[0051] —Evaluation of Multilayer Coating Film—

[0052] A multi-angle spectrophotometer (GCMS-4 by MURAKAMI COLOR RESEARCH LABORATORY CO., Ltd.) was used to measure the spectral reflectance of the multilayer coating films of the first and second examples and the comparative example. The wavelength measurement ranged from 400 nm to 700 nm. Measurement results are shown in FIG. 8.

[0053] The first and second examples have a flat (substantially constant) spectral reflectance curve over the entire wavelength of 400 nm to 700 nm, and feature no red or yellow color development. The comparative example has a spectral reflectance curve, which becomes higher at a wavelength ranging from 600 nm to 700 nm inclusive, and features red or yellow color development.

[0054] Further, the lightness of highlights (Y value)(3°) and shade (L* value)(110°) of the multilayer coating films of the first and second examples and the comparative example have been measured. (These coatings feature a huge disparity around highlights of 3°. When expressing the highlights with the L* value, however, the value of 100—which is the upper limit of the L* value—is exceeded. Therefore, the highlights are expressed with the Y value.) Results are shown in Table 4.

TABLE-US-00004 TABLE 4 Y (3°) L* (110°) First Example 421.2 2.21 Second Example 290.2 4.67 Comparative Example 98.1 6.38

[0055] The first and second examples feature a strong contrast between highlights and shade, which shows that a color development with a strong effect of light and shade (high-contrast) has been obtained. In particular the first example, where the base layer is black, features a big difference in lightness between highlights and shade.

DESCRIPTION OF REFERENCE CHARACTERS

[0056] 1 Structure [0057] 2 Primary Particles [0058] 11 Automobile Body (Steel Plate) [0059] 12 Multilayer Coating Film [0060] 13 Electrodeposition Coating Film [0061] 14 Black Base Layer [0062] 15 Bright Layer [0063] 16 Colored Layer (Black) [0064] 17 Transparent Clear Layer [0065] 21 First Black Pigment [0066] 22 Bright Material (Aluminum Flakes) [0067] 23 Second Black Pigment (Fine Carbon Black)